1. Field of the Invention
The present invention relates to a thermal transfer image-receiving sheet on which an image can be formed by means of thermal transfer printing. More particularly, the present invention relates to a thermal transfer image-receiving sheet comprising a seal part including at least a receptive layer, a substrate and a pressure-sensitive adhesive layer which are laminated in the order mentioned, and a release sheet (releasing part) which is separably adhered to the pressure-sensitive adhesive layer of the seal part, and to a process for producing such a thermal transfer image-receiving sheet.
2. Description of Related Art
Up to the present time, there have been known a variety of thermal transfer methods. These thermal transfer methods are effected in the following manner: a thermal transfer printing sheet having a colored transfer layer that is formed on a substrate sheet is superposed on the surface of a thermal transfer image-receiving sheet; and heat is applied image-wise to the back surface of the thermal transfer printing sheet by using a thermal head or the like, thereby thermally transferring the colored transfer layer of the thermal transfer printing sheet to the surface of the thermal transfer image-receiving sheet to form thereon an image.
These thermal transfer methods are roughly classified into two types, that is, sublimation transfer type and hot-melt transfer type, depending upon the constitution of the colored transfer layer to be used. Both printing methods of these two types can achieve the formation of full-color images. For instance, transfer printing sheets of three or four colors of yellow, magenta and cyan, and, optionally, black are prepared; and images of these colors are formed one over the other or sequentially by means of thermal transfer printing on the surface of a thermal transfer image-receiving sheet to form thereon a full-color image.
Thanks to the development of hardware and software associated with multimedia, these thermal transfer methods are expanding their market as full-color hard copying systems for computer graphics, still pictures transmitted via satellite communication, digital images represented by those images stored in CD-ROM or the like, and analog images such as video-taped images.
Thermal transfer image-receiving sheets on which images will be formed by these thermal transfer methods have various practical applications. Typically, they can be used as proof sheets, and as recording sheets for output images, output plans or designs drawn by CAD/CAM or the like, or images output from a variety of medical analyzers or measuring instruments such as CT scanners and endoscopic cameras. They can also be used as the alternative of instant photo, and as paper for producing ID cards, credit cards, and other cards on which facial photos, etc. will be printed, or for producing synthetic or memorial photos which are taken at amusement facilities such as recreation parks, game centers, museums, aquariums and the like.
Further, a thermal transfer image-receiving sheet that can be adhered to any object has also come to be used with the diversification of applications of thermal transfer image-receiving sheets as described above. Such a thermal transfer image-receiving sheet comprises, for example, a seal part including a receptive layer in which an image will be formed, a substrate and a pressure-sensitive adhesive layer which are laminated in this order, the seal part being separably combined to a release sheet through the pressure-sensitive adhesive layer. This is a thermal transfer image-receiving sheet of so-called label or seal type. This thermal transfer image-receiving sheet is used in the following manner: after forming a desired image on the receptive layer, the seal part including the receptive layer is separated from the release sheet, and this seal part separated is adhered to an object through the pressure-sensitive adhesive layer.
As shown in FIGS. 8 and 9 (figures showing the present invention), a thermal transfer image-receiving sheet 1 includes a plurality of sections, and each section is provided with a rectangular half cut 2. An image 10 is formed in each section, so that a plurality of images 10 are located on one thermal transfer image-receiving sheet 1.
The thermal transfer image-receiving sheet 1 shown in FIGS. 8 and 9 includes a seal part 9 including a receptive layer 8, a substrate 7 and a pressure-sensitive adhesive layer 6 which are laminated in the order mentioned, and a release sheet 5 which is separably adhered to the pressure-sensitive adhesive layer 6 of the seal part 9. In this thermal transfer image-receiving sheet 1, the half cut 2 penetrates the layers of the seal part 9 and reaches to the top of the release sheet 5. After an image 10 is formed in each section that is defined by the half cut 2 formed in the seal part 9, a part of the seal part 9 is separated from the release sheet 5 along the half cut 2. This seal part 9 separated can be adhered to any object 11 (see FIG. 10 (figure showing the present invention)).
An image can be formed on the above-described thermal transfer image-receiving sheet in the following manner. The thermal transfer image-receiving sheet is firstly fed to a thermal transfer printer; a detector installed in the thermal transfer printer detects the position of the end of this image-receiving sheet. Since information concerning the position of the half cut has been stored in the thermal transfer printer, the thermal transfer image-receiving sheet is carried so that the half cut comes to the right position relative to the thermal head; and an image is then formed.
However, when an image is formed in the above-described manner, various troubles tend to be caused at those parts of the thermal transfer image-receiving sheet where half cuts have been formed (hereinafter referred to as xe2x80x9chalf-cut-provided partsxe2x80x9d). Specifically, the half-cut-provided part lifts to cause, while printing is being conducted by using a thermal head, such troubles that the seal part is unfavorably separated at the raised part and that the pressure-sensitive adhesive agent runs off from the seal part to stick to a thermal transfer printing sheet.
Further, when the thermal transfer image-receiving sheet that is curled is carried by a thermal transfer printer or the like, or when heat is applied, by a thermal head, to the thermal transfer image-receiving sheet to print thereon an image, the seal part is unfavorably separated from the release surface of the release sheet at the half-cut-provided part. In particular, when the section on which an image will be formed is small, even such a trouble is caused that the seal part falls off.
The present invention was accomplished in the light of the aforementioned problems. An object of the present invention is therefore to provide a thermal transfer image-receiving sheet free from the lifting of the half-cut-provided parts formed in on the seal part of the thermal transfer image-receiving sheet, which tends to cause, while printing is being conducted by using a thermal head, such troubles that the seal part is unfavorably separated at the raised part and that the pressure-sensitive adhesive agent runs off from the seal part to stick to a thermal transfer printing sheet; and a process for producing such a thermal transfer image-receiving sheet.
Another object of the present invention is to provide a thermal transfer image-receiving sheet free from such a problem that the seal part is unfavorably separated from the release sheet when the thermal transfer image-receiving sheet is carried by a thermal transfer printer, or when printing is conducted by using a thermal head; and a process for producing such a thermal transfer image-receiving sheet.
The first aspect of the present invention is a thermal transfer image-receiving sheet comprising: a seal part including at least a receptive layer, a substrate and a pressure-sensitive adhesive layer which are laminated in the order mentioned; and a release sheet which is separably adhered to the pressure-sensitive adhesive layer of the seal part, wherein the seal part is provided with a half cut for separating a part of the seal part from the release sheet and wherein the half cut has a groove width of 25 to 60 xcexcm.
In the above-described first aspect of the present invention, it is preferable that the shearing force of the pressure-sensitive adhesive layer of the seal part, measured in accordance with JIS (Japanese Industrial Standards) Z0237-3 be in the range of 800 to 1600 gf.
The second aspect of the present invention is a thermal transfer image-receiving sheet comprising: a seal part including at least a receptive layer, a substrate and a pressure-sensitive adhesive layer which are laminated in the order mentioned; and a release sheet which is separably adhered to the pressure-sensitive adhesive layer of the seal part, wherein the seal part and the release sheet are adhered to each other so that they show continuous and slight changes in peel strength when the seal part is separated from the release sheet.
In the above-described second aspect of the present invention, it is preferable that the slight changes in peel strength measured by the 180 Degrees Peeling Method according to JIS Z0237-8.3.1 be in the range of 1 to 10 g/cm. It is also preferable that the mean peel strength be from 10 to 75 g/cm. Further, it is preferable that the release surface of the release sheet be roughened. It is also preferable that the release sheet is composed of a release layer which is in contact with the pressure-sensitive adhesive layer, and a release substrate which supports the release layer, and wherein either the release layer or the release substrate be roughened.
Furthermore, in the second aspect of the present invention described above, it is preferable that the seal part be provided with a half cut for separating a part of the seal part from the release sheet. The groove width of the half cut is preferably from 25 to 60 xcexcm.
The third aspect of the present invention is a process for producing a thermal transfer image-receiving sheet, comprising the steps of: preparing a thermal transfer image-receiving sheet including a seal part including a receptive layer, a substrate and a pressure-sensitive adhesive layer which are laminated in the order mentioned, and a release sheet which is separably adhered to the pressure-sensitive adhesive layer of the seal part; and putting a cutter blade in the seal part of the thermal transfer image-receiving sheet to form a half cut with a groove width of 25 to 60 xcexcm, for separating a part of the seal part from the release sheet.
In the above-described third aspect of the present invention, it is preferable that the nose angle of the cutter blade be in the range of 25 to 500xc2x0 and that the nose length of the same be greater than the thickness of the seal part.
According to the first and third aspects of the present invention, the half cut for separating a part of the seal part from the release sheet is formed so that the groove width of the half cut will be from 25 to 60 xcexcm. Therefore, such troubles can be prevented that the half-cut-provided part lifts to cause, while printing is being conducted by using a thermal head, the unfavorable separation of the seal part from the release sheet, or the running off of the pressure-sensitive adhesive agent from the seal part to stick to a thermal transfer printing sheet.
According to the second aspect of the present invention, the seal part and the release sheet are adhered to each other so that they show continuous and slight changes in peel strength when the seal part is separated from the release sheet. Therefore, such a trouble can be avoided that the seal part is unfavorably separated from the releasing part while a thermal transfer printer is carrying the thermal transfer image-receiving sheet, or when printing is conducted by using a thermal head.